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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: ForumUserGF on May 17, 2018, 12:39:58 AM

Title: How to calculate the voltage of an alkaline battery?
Post by: ForumUserGF on May 17, 2018, 12:39:58 AM

I just cannot get a voltage of 1.5V as the result. Here is what I have so far:

Code: [Select]

U = E0(cathode) – E0(anode)
 = 1,23 V - (-1,2 V)
 = 2,43 V
But this cannot be correct...

Title: Re: How to calculate the voltage of an alkaline battery?
Post by: sjb on May 17, 2018, 04:06:55 AM

Well, the maths is right, but without seeing where this has come from, I'm not sure how to comment.

Title: Re: How to calculate the voltage of an alkaline battery?
Post by: ForumUserGF on May 17, 2018, 11:12:55 AM

Quote from: sjb on May 17, 2018, 04:06:55 AM

Well, the maths is right, but without seeing where this has come from, I'm not sure how to comment.

Well,

Oxydation: Zn + 4OH^-   :rarrow:  [Zn(OH)₄]^2- + 2e^-
Reduction: 2MnO₂ + H₂O + 2e^-  :rarrow: Mn₂O₃ + 2OH^-

And now you take E0(Mn²⁺/MnO₂) = 1,23V and E0(Zn/Zn(OH)₄^2-) = -1,199V. However, the result is wrong.

Title: Re: How to calculate the voltage of an alkaline battery?
Post by: sjb on May 17, 2018, 12:45:29 PM

If the reduction is MnO₂  :rarrow: Mn₂O₃ why are you using E° for a different half reaction?